Often it is important to quickly and accurately determine the level and type of chemical compounds present on the surface of a material. For example, it may be desirable to quickly and reliably test for the presence of toxic industrial compounds (TICs), illegal drugs, explosive compounds, or chemical or biological weapons or substances. Some substances have a fairly high volatility. Many TICs have ambient temperature vapor pressures greater than 0.5 T (mmHg). Others, for example various explosives such as nitroglycerin, trinitrotoluene (TNT) and ethylene glycol dinitrate (EGDN), have ambient temperature vapor pressures below 0.05 T.
Various technologies have been proposed for surface contamination sampling. For example, mass spectrometry has long been used to accurately determine the presence of initially unknown chemical and biological samples. Usually a sample is vaporized for transport via gas phase flow to the analyzer and ionized, with the resulting ions being measured to determine a mass to charge ratio spectrum which is, in turn, used to identify the basic constituents of the original sample. Due to the large size and power requirements of most mass spectrometers, they have typically been housed in a dedicated laboratory. As such, samples were collected at a potentially contaminated site and brought to the mass spectrometer for analysis. This tended to be a time consuming and expensive endeavor, especially if the surface being analyzed was located a distance from the laboratory.
In order to address the problem of analyzing samples at a contamination site, portable field detection systems have been developed. For example, Bruker Daltonics manufactures portable mass spectrometers such as the MM series and the EM series. With some mass spectrometers, a sample to be tested is collected and placed in a test chamber, where it is exposed to heat and a carrier gas to volatilize and transport molecules to a mass spectrometer detection unit. Other mass spectrometers, such as Bruker Daltonics MM1 and MM2 models, utilize a sampling head or probe that is brought into contact or proximity with a surface to capture volatilized molecules from the surface and transport them to a substance detector such as a mass spectrometer. Various sampling heads or probes have been proposed in the art, see U.S. Pat. No. 4,433,982, U.S. Pat. No. 4,541,268, and/or U.S. Pat. No. 5,517,026. Such sampling heads utilize a membrane that is permeable to the volatile molecules of interest, and apply heat to the membrane when it is placed in contact or proximity to the surface being tested in order to assist in volatilization of the molecules so that they diffuse into the membrane. A carrier gas on the back side of the membrane then carries the volatile molecules to a substance detector such as a mass spectrometer. Known sampling heads, however, have limitations on their operating temperature ranges, particularly on the upper end, which limits their effectiveness on testing for a wide variety of substances potentially of interest, especially substances with low vapor pressures, and/or their use for testing high temperature surfaces. Attempts have been made to enhance the ability of silicone sampling membranes by incorporating fillers such as ferric oxide into the polymer matrix; however, this can have deleterious effects on product performance such as imputing reactivity and/or reducing analyte throughput for some analytes. Additionally, the effectiveness of transmission through the membrane is a function of analyte vapor pressure, analyte solubility in the membrane material and analyte mobility through the membrane material. All of these properties are, in turn functions of temperature and obtaining optimum, or even satisfactory, performance over a wide range of analyte volatility has been impracticable.
Accordingly, there continues to be a need in the art for sampling devices that are capable operating under a wide range of operating conditions and/or for sampling for the presence of a wide range of compounds, including both compounds of low volatility that require substantial heating to collect and compound of high volatility that are more effectively captured via whole air sampling.